The invention relates to a magnetic head comprising a magnetic core provided with pole tips which limit a gap having a small length and filled with non-magnetizable material which adheres these pole tips to each other, and further to a method of manufacturing such a magnetic head.
Such a magnetic head is known from U.S. Pat. No. 3,656,229 and can be used for recording, reproducing and/or erasing magnetic information in a track of a magnetic information carrier.
The gap in the magnetic core is of essential importance for the quality of a magnetic head: the length of the gap should be small to very small dependent upon the envisaged application of the magnetic head, while also the permissible tolerance of the gap length is very small. In magnetic heads for video-recording, in which information carriers of the longitudinal magnetization type are used, a gap length of approximately 0.25 .mu.m is aimed at; in the case of an information carrier of the perpendicular magnetization type, a gap length of approximately 0.1 .mu.m is aimed at. Furthermore, the material with which the gap is filled and the adhesion of this material to the gap-limiting surfaces of the pole tips are important for the durability of the magnetic head.
The term "gap length" is to be understood to mean herein the dimension of the gap which corresponds to the distance between the gap limiting surfaces of the pole tips.
According to U.S. Pat. No. 3,656,229, magnetic heads are obtained by providing on a magnetic core part a layer of a non-magnetic metal oxide or metal oxide mixture as a material filling the gap and determining the length of the gap. The core part is heated for this purpose to a comparatively high temperature (400.degree.-800.degree. C.) in contact with the vapour of one or more organometallic compounds. A second core part, which may be provided with such a metal oxide layer, is adhered to the first part by means of an adhesive. Examples of adhesives are glass and synthetic resins, but the patent gives preference to glass because synthetic resins would swell to an undesired extent. In order to unite the core parts, they are arranged opposite each other and molten glass is caused to flow into the slit between these core parts. The magnetic heads obtained have a gap length of 0.8-1.2 .mu.m.
For many applications, this gap length is too large. Other disadvantages of these known magnetic heads are that the metal oxide layer is deposited from the gaseous phase at a high temperature. In the manufacture of magnetic heads, this step is time-consuming and expensive, while the step of filling the slit between two core parts with molten glass is difficult to control. It is moreover desirable to provide both core parts with a metal oxide layer in order to prevent interaction between the glass and a core part not coated with metal oxide. In this magnetic head, the gap consequently has a filling composed of two or three layers. The accuracy with which the gap length is adjusted therefore depends in this known magnetic head upon the accuracy with which the desired thickness of each of the two or, in the preferred case, three layers is obtained.